The 357 sig was developed from a 40 S&W case. The short neck and smaller case do not work with heavy bullets like the 357 mag uses. Heavy bullets (longer) would create very hi pressure if loaded to the required overall length. To shoot heavy bullets you would have to start with a 10 mm case, but then you would not be able to use guns designed for the 9mm or 40 S&W cartage length. The 357 sig is very good at what it was designed to do, compete with the 125 gr. 357 mag load.
